Angry crowds took to the streets of India’s Bihar state to protest over the deaths of at least 22 school children who ate poisoned food provided through a scheme monitored under a £25m UK government programme.

The children fell ill after eating a meal of rice with soybeans and potatoes prepared with oil apparently contaminated with insecticide.

The headmaster of the school – located around 25km from the city of Chhapra in the Saran district of Bihar – is reported to have fled the school when the children started vomiting. Police have registered a case of criminal negligence against him.

Furious parents besieged the local police station after the children started to fall ill, protesting that many would have survived had the school acted more quickly to provide medical assistance. At least 80 other children from the Navsrijit Primary School were affected by the outbreak, with several said to be in a critical condition.

Reports locally said that there had been previous poisoning cases in the area linked to the Midday Meal programme, one of the key planks of the Indian government’s anti-poverty strategy. The Midday Meal Scheme in Bihar is monitored by the UK government through a £25m grant from the Department for International Development (DfID) for its Poorest Areas Civil Society Programme Phase II, which is due to run until 2015.

The DfID programme is intended to help eight million people from the poorer elements of Indian society in seven states, including Bihar, through grants and capacity-building support to civil society organisations. A DFID spokesman said UK money did not directly fund the scheme but helped to monitor the way it was implemented: “DFID does not fund the Midday Meal Scheme in Bihar. Our support to PACS helps communities to effectively monitor the implementation of the scheme.”

Oxfam India demanded a full investigation into the deaths and said it had previously raised concerns about the programme “because of lack of funds, poor quality food and highly inadequate monitoring of just a handful of schools once or twice a year.”

The dead were reported to include two children of one of the school cooks. Last night there were still fears that the death toll would rise. One school cook is also reported to be receiving hospital treatment. One 12-year-old pupil, Savita, said that she suffered a stomach ache after eating the meal and started to be sick. “I don’t know what happened after that,” she said.

Raja Yadav, the father of one young victim, said: “As soon as my boy returned from school, we rushed to the hospital with him.”

Initial tests suggested that the food had been contaminated with an organophosphate chemical used as an insecticide on wheat and rice crops.

Suspicions fell on a new type of cooking oil used to prepare the meal. State education minister PK Shahi said the school cook had told him the oil looked “discoloured and dodgy” but her concerns were ignored by teachers who said it was safe. Some teachers also suggested the food may have been stored in contaminated containers.

R K Singh, the medical superintendent at the children’s hospital in the state capital, Patna, said: “We feel that some kind of insecticide was either accidentally or intentionally mixed in the food, but that will be clear through investigations. We prepared antidotes and treated the children for organic phosphorous poisoning.”

The opposition BJP party criticised the time it took for children to be taken to hospital. “It took 15 hours to evacuate kids, it’s only after 17 kids died the authorities decided to shift them at midnight,” said BJP leader Pratap Rudy.

Protesting villagers set four police vehicles alight and police reinforcements had to be drafted in as anger spilled over. The state has offered compensation of Rs 200,000 for each child who died.